A disadvantage of conventional polygraphy is the inferential nature of its methods. The sympathetic nervous system responses that are measured by the polygraph are not specific to deception. Conventional polygraphy for the detection of deception relies on psychophysiological measures of the sympathetic nervous system response, such as respiration rate, heart rate, and electrodermal activity, to detect anxiety associated with guilt or lying. These autonomic responses are common to any number of emotional, as well as cognitive and physiological responses. Because these psychophysiological responses are not specific to deception, the polygrapher does not actually measure deception per se. Rather, the polygrapher must infer deception based on differential psychophysiological responses to well-designed questions. Thus, conventional polygraphy suffers from a lack of specificity in differentiating guilt from fear or anxiety, and even anger, which can contribute to an unacceptably high level of false positives. Further, conventional polygraphy is subject to various inherent sources of variability, such as personality factors relating to the examiner and examinee, the question format, and the decision rules, for example.
Further, the relatively quick habituation of the autonomic measures used in conventional polygraphy, as well as the pain that results from extended occlusion of the blood supply by the blood pressure cuff, prevent the repetition of critical (e.g., the questions to which the examinee might be expected to lie) and comparison or control questions. As a result, in conventional polygraphy, the number of times critical questions can be repeated is limited (e.g., three times) because the ability to accurately infer a deceptive response diminishes with repetition.
Due to the lack of acceptable reliability, and specificity in particular, of conventional polygraphy, recent efforts to increase the reliability of credibility assessment have turned to more direct measures of central nervous system function during credibility assessment. Rather than assessing the psychophysiological correlates of guilt, anxiety, or even pleasure associated with deception, e.g., the emotional response to lying or to the fear of being caught, neuroimaging has been utilized to assess the neural pathways that underlie the cognitive as well as the emotional aspects of deception. In one known neuroimaging technique, encephalography, or EEG, voltage oscillations that reflect the neural activity associated with various cognitive and emotional events are measured. A disadvantage of measuring these voltage oscillations is that the relative spatial resolution is poor. Further, high-density electrode arrays are typically needed to localize activation sources.
Although central nervous system function has the potential to be more accurate than conventional polygraphy, it is widely held that there is no specific “deception circuit” in the brain, i.e., a set of neurons that are only activated when being deceptive, and not activated under any other circumstance.
Other attempts to identify the neural underpinnings of conscious deception comprise functional magnetic resonance imaging. Functional magnetic resonance imaging, however, is expensive, highly sensitive to motion artifacts, and confines participants to restricted positions. Also, U.S. Patent Application Publication No. 2006/0058683, which is a continuation in part of U.S. patent application Ser. No. 10/618,579 suggests an optical system for the detection of deceit.